The present invention is generally related to magnetoresistive heads used in disk drive systems for recovering data stored on magnetic disk. In particular, the present invention relates to an apparatus for compensating for the non-linear response to flux exhibited by magnetoresistive head.
Magnetoresistive heads are read only devices that are being used in both flexible and rigid magnetic memory systems, such as disk drive system, to recover data recorded on the magnetic media of the magnetic memory system. Magnetoresistive heads respond to the magnitude of the flux being sensed by the magnetoresistive head where inductive heads respond to the rate of change in flux being sensed by the inductive head. This is one of the characteristics of the magnetoresistive head that have resulted in an increase in the areal density that data can be recorded on the magnetic medium over that which was previously realized using inductive heads.
The magnetoresistive head has a non-linear response to the magnitude of flux as a function of the orientation of the flux. This results in the signal generated by the magnetoresistive head being asymmetrical, that is the magnitude of the positive portion of the signal will be different than the magnitude of the negative portion of the signal with all other factors being constant except for the orientation of the flux. The asymmetry of the signal further causes a baseline shift in the signal due to the AC coupling employed in recovering the signal generated by the magnetoresistive head.
The combined effect of the asymmetry and baseline shift in the signal can cause a data detector, which recovers the data from the signal, to have an increase in the number of errors in the decoded data because typical data detector assumed a symmetrical signal with no baseline shift.
Many disk drive systems use a digital data detector to recover the data from the analog signal generated by a magnetoresistive head. In such systems, an analog to digital (A/D) converter is used to convert the analog signal into a series of digital signals which will be used by a data detector to detect the data encoded in the analog signal. The value of the digital signal is affected by the asymmetry and the baseline shift of the analog signal being sampled such that the value of the digital signal produced from the analog signal being sampled can have a different value than the digital signal would have had if the analog signal was symmetrical and had no baseline shift. The digital detector expects the output of the analog to digital converter to produce digital signals having specified values based upon a symmetrical analog signal with no baseline shift being provided to the analog to digital converter. The resulting differences in value of the digital signals produced by the analog to digital converter in response to an asymmetrical analog signal having a baseline shift can cause the data detector to erroneously interpret the digital signal produced by the analog to digital converter.